Close all other applications to resolve software conflicts and free up resources
Reset your user interface to make sure your files and addons are not corrupted, potentially causing them to use a large amount of memory
If you are almost out of storage space, your computer can suffer memory management issues. Try clearing some space on your storage drive
If all else fails, try uninstalling and reinstalling the game
Retail opens correctly, are they suggesting to reinstall +30gig b/c something went wrong at their end?